Method and apparatus for coating a core material with metal

ABSTRACT

Apparatus and method for coating a high tensile strength fibrous material with an extrudible, corrosion-resistant metal to form a composite, continuous wire using dies, a compression cylinder in fluid connection with the dies, a piston for forcing the metal out of the compression cylinder and through the dies and a mechanism for feeding a fibrous material through the dies as the metal coating is extruded out the dies with the fiber. Continuous lengths of a composite material made by such a method, electrode grids comprised of the composite material made by such a method and a cabled composite wire constructed of the composite material made by such a method. Also, series and parallel connected cells comprising a battery utilizing such electrode grids.

The present application is a continuation-in-part application ofco-pending application Ser. No. 643,676, filed on Aug. 22, 1984, nowabandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for coatingmetal wire or fibrous materials with metal. The invention relates alsoto a scrim which may be woven from such a composite wire and the use ofthe scrim in the electrodes of electrochemical cells. More particularly,the present invention relates to a method and apparatus capable ofproducing continuous lengths of fine composite wire comprised either ofmetal wire coated with an extrudible, corrosion-resistant metal or afibrous core material coated with an extrudible, corrosion-resistantmetal such as lead, the weaving of that composite wire into a scrim, andthe use of that scrim as an electrode grid in an electrochemical cell.

Conventional batteries include electrodes having metallic substrates onwhich a layer of active material is deposited. The battery may containseveral pairs of positive and negative electrodes, stacked, rolled orsuspended within a battery case and covered by the electrolyte containedwithin the battery case. Most conventional rechargeable batteries are ofthe lead acid type. The electrode grids of conventional lead acidbatteries are coated with an active material, usually a lead oxide. Theactive material in the negative electrode contains expanders which allowthe plate to become spongy when it is formed. A "forming" charge isapplied to both positive and negative plates to convert the layer ofactive material on the positive plate to a porous oxide of lead and thelayer of active material on the negative plate to sponge lead.

Conventional state of the art lead acid batteries are relatively heavy,causing the battery to have a low specific energy. The specific energyof some commercially available, state of the art lead acid batteries ison the order of about 14 watt hours per pound at the three hourdischarge rate. The heavy weight of the battery is a direct consequenceof the use of large amounts of lead in the electrodes, both in the gridand in the active material, and in the connectors and straps, or busbars, of the battery.

Thick lead grids are required for several reasons. For instance, theactive material usually takes the form of a paste which is cured ontothe grid. Although the paste adheres well to itself, it does not adherewell to the electrode grid, particularly during repeatedcharge-discharge cycles. Because of this characteristic, the grid mustbe made more substantial so that it can act as a latticework to helpsupport the active material.

Further, the electrode grid itself is relatively fragile, necessitatinga construction which is heavier than needed for the grid to perform itselectrical function. The grid used in many conventional lead-acidbatteries is formed either by casting liquid lead into a mold of thedesired configuration or by expanding sheet lead into a mechanicallystiff grid. The grid is then assembled into the electrode assembly.

During the manufacture of the electrode, its handling, and its assemblyinto the battery, it is subjected to a number of mechanical stresses.Once assembled into the battery, the electrode will be subjected to anumber of induced stresses. The primary source of manufacturing stressis the pasting operation, during which the paste of active material istroweled onto and into the grid. As it is troweled into and onto thegrid, the paste, which is heavy and relatively stiff (i.e., not veryplastic), tends to bend, stretch and tear the latticework. Thisdeformation of the grid structure results in many points at which thelead in the grid is stressed, and it is at these stress points wherecorrosion will occur first and proceed at the fastest rate. Thus,expanded metal grids, which offer the advantage of being lighter thancast grids, are inherently susceptible to accelerated stress corrosionbecause each point at which the metal sheet was expanded represents astress point.

The induced stresses are the result of factors such as volumetric growthand shrinkage of the electrode during battery charge and dischargecycles, sagging of the conductors due to the pull of gravity on theheavy mass of active material which they support, and, if the battery isused in an application such as in an automobile, vehicle shock, thermalcycling, and vibration. Mechanical failure of the electrode occurs whenthe mechanical and induced stresses to which the electrode is subjectedexceed the tensile and/or shear strength of the materials comprising theelectrode. To help prevent premature mechanical failure of theelectrodes due to these stresses, it is necessary to manufacture them inthicknesses which enable them to withstand the stresses to which theyare likely to be subjected. Because so much lead must be used to providethe thickness which enables the grid to withstand these stresses,conventional grids have cross-sectional dimensions that are much largerthan is required for actually conducting electrical current. The resultof the use of thick grids is a battery which is relatively heavy, andhas a low specific energy and material utilization factor.

In addition to a thick grid, a thick coating of active material on theelectrodes is necessary to increase battery capacity. The thick coatingis necessary because, as a general rule, the thicker the layer of activematerial, the greater the capacity of the battery to store electricalenergy.

As the volume (and weight) of active material is increased and theweight of the battery case, straps, posts and grid conductors remainsrelatively constant, the utilization of the active material is increasedon a per unit weight basis. This increased utilization results in anincrease in the specific energy of the battery. However, the activematerial utilization factor of many state of the art lead acid batteriesis only approximately 50-55% of battery weight.

The thickness of the layer of active material requires that the gridlatticework be strong enough to support this thicker layer of activematerial. Because of the relatively low tensile strength of pure lead,it is necessary to make the lead grids substantially thicker than wouldbe necessary to enable them to serve their electrical function so thatthe grids will withstand the above-described mechanical and inducedstresses.

There are limits to the thickness of the layer of active material. Onelimitation is imposed by the weight of the active material. Anotherlimitation is a result of the electrical characteristics of the activematerial. The active material on the positive electrode is asemiconductor, that is, due to its own internal resistance, it iscapable of conducting electricity only a relatively short distancethrough itself. Consequently, the thickness of the active material islimited to that distance through which the active material is capable ofefficiently conducting current. This characteristic of the activematerial is one reason for the presence of the grid conductor in thepositive electrode. The grid conductor serves the function of conductingthe current generated in the active material out of the active material.

The thickness of the layer of active material is also limited by therelative inability of the active material to adhere to the grid duringcharge-discharge cycling and by its low tensile strength. As a result ofthese characteristics, the above-described mechanical stresses oftencause the grid to prematurely shed the fragile active material.Additional battery weight results from the fact that precautions must betaken to prevent any active material from floating loose in theelectrolyte in the cell and shorting out the battery. The electrodes maybe provided with special glass compression pads to compress the activematerial against the grid, thereby preventing a short circuit in thecell, but also adding to the weight of the battery without improvingbattery capacity.

As a result of these factors, most of the batteries available to daterepresent a balance between durability, capacity and specific energy,with certain of these factors being optimized for certain applications.For instance, in applications in which the weight of the battery is themost important concern, the electrodes are manufactured with thethinnest layer of active material practical and grids are pared down asmuch as is made possible by the reduced thickness of the activematerial. A battery with a thin layer of active material and relativelylight weight grids represents a trade-off of increased manufacturingcosts, shorter battery life and lower capacity for lighter batteryweight.

Another problem, also related to the weight, bulk and capacity of leadacid batteries is the fact that these factors make it difficult toconstruct a rechargeable battery in flashlight battery sizes, i.e., "Dcells", "C cells" and so on down to "AAA cells" and smaller, specialpurpose batteries. Spiral wound lead acid cells are easily connected inseries to form batteries, which are available in sizes ranging from "BC"to "D." These cells produce high currents and are constructed from leadgrids which are die cut from a flat sheet of pure lead which is rolledinside the round battery case in a tight spiral. Each spiral grid has arelatively large surface area, and there is no need to connect severalsmall grids in parallel as in a conventional battery, resulting in asavings in weight and the cost of manufacture, and these cracks arehighly susceptible to attack by the acid, causing the rapid corrosion ofthe grid.

However, no cells in sizes below "D" are available commercially becasethe soft, thick (about 0.04 inches) grid used in these cells cannot berolled into a spiral which is tight enough to be used in batteries ofsmaller diameter. Cracks and stress points form on the grids ofbatteries of this size because the radius of curvature of the gridexceeds that associated with the maximum strength of the lead. Thesecracks are highly susceptible to attack by the acid of the battery,resulting in the rapid corrosion of the grid.

These same problems are involved in the construction of conventionalnine volt rechargeable batteries. At present, the only readilyavailable, multi-purpose rechargeable nine volt battery is constructedof nickel and cadmium (the "nicad" battery). This battery contains six1.25 volt cells and produces about 7.5 volts. It is unusuable for somenine volt applications because of its low voltage. However, the moreserious limitation of the nicad battery is its so-called "memory". Anicad battery which is repeatedly discharged at low currents willoccasionally "forget" that it is capable of delivering high currents, aresult of the chemical conditions within the cells. Although reversible,this characteristic results in the decrease of the life of the batteryif the battery is left on float or standby charge for indefiniteperiods.

There have been many attempts to improve upon the basic scheme governingthe construction of electrochemical cells. One approach attempts to makeadvantageous use of the fact that the outer surface (approximately theouter 5×10⁻³ inches) of the lead grid element provides all theelectrical conductivity and surface area required for attachment of theactive material. Hence, most of the lead in a conventional electrodegrid does not participate in the electrochemical function, but merelyprovides the strength and stiffness for the grid to survive itsenvironment and manufacturing stresses. This approach is characterizedby the building of electrodes which provide only an outer layer of leadon the grid element by depositing a layer of lead on a substrate whichpossesses the desired properties of light weight and high mechanical andchemical durability.

This approach is exemplified by, for instance, U.S. Pat. No. 4,275,130.This patent discloses a battery in which the electrodes take the form ofparallel stacked biplates composed of a thermoplastic material such aspolypropylene with conductive fibers of carbon or metal embedded in itto serve as strengthening and conducting elements. Each biplate isprovided with parallel stripes of lead in electrical contact with theconductive fibers to serve as a grid. The active material is heldbetween thin, porous glass mats, and the stacked assembly is thenaxially compressed and assembled into the battery case.

This approach is also exemplified by U.S. Pat. No. 3,808,040, whichdiscloses a method of manufacturing battery plate grids which involvesthe strengthening of a conductive lattice work to serve as a gridelement by depositing strips of synthetic resin on the lattice work.This patent is hereby incorporated into the present disclosure byreference thereto.

U.S. Pat. No. 3,973,991, incorporated herein by reference thereto,discloses a light-weight electrode assembly comprised of at least threelayers. The center layer, or grid, is formed of a thin, perforated sheetof a conductive metal such as lead, and the layers on either side of thegrid are comprised of a paste of active material with short syntheticfibers or a mixture of synthetic and natural fibers suspended in thepaste to help hold it together. The disclosure of this patent indicatesthat the center, conductive layer may be as much as 90% open area.However, a lead grid with this much open area might be much too fragileto manufacture at reasonable cost or to use in many applications, a factwhich is implicitly recognized by the examples set forth in thedisclosure of that patent which describe a thin layer of onlyapproximately 56% open area.

U.S. Pat. No. 3,556,855 discloses a grid element comprised of anelectrically conductive resin and metal coated glass fibers. The fibersare of short length, are dispersed in the resin, and have a layer of anelectrically conductive metal deposited on them according to methodsknown in the art. Only silver, copper and nickel-coated glass fibers aredisclosed by this patent, which is hereby incorporated herein byreference thereto.

U.S. Pat. No. 4,091,183 discloses a solid plate lead core grid with aspecial surface profile. This grid element is comprised of a solid coreof lead sandwiched between two porous envelopes which contain the activematerial of the electrode and are provided with a special surfaceconfiguration. Electrodes of this type are assembled into a batterywhich is capable of resisting plate deformation during hard and deepdischarges, but which represents no weight or capacity advantage.

This approach is also represented by U.S. Pat. No. 3,560,262, whichdiscloses a non-woven nylon wafer with a thick coating of conductivemetal electroplated onto it for use as a grid in the electrodes ofalkaline batteries. The nickel hydroxide or cadmium hydroxide activematerial is deposited into the pores of the conductive metal.

Other attempts to improve on the prior art batteries have focused on theactive material. For instance, U.S. Pat. No. 3,466,193 discloses apositive electrode comprised of a paste of lead dioxide containing 5-25%weight short lead fibers, spaced throughout the paste such that thefibers do not contact each other. The fibers are of relatively shortlength and are obtained by chopping lead wool. This paste is depositedon a frame made of a plastic resin to form the positive electrode, whichis then assembled to a negative grid and inserted into the battery case,resulting in a battery which contains only about 29% less lead than manyconventional batteries and which has a somewhat improved specificenergy.

U.S. Pat. No. 4,110,241 discloses a method for making an active materialreinforced with synthetic fibers. This reinforcement may increase thedurability of the battery, but has little effect on its capacity orspecific energy.

Similar problems of battery life, capacity and weight are encountered inother types of batteries, and attempts to improve these batteries, forthe most part, represent adaptations of the above-described balancingformula to the specific type of battery. For instance, U.S. Pat. No.3,770,507 discloses a resinous grid impregnated with lead dioxide andsynthetic fibers for use in non-rechargeable primary batteries usingfluoroboric acid as an electrolyte. U.S. Pat. No. 3,397,088 discloses anelectrode that is enveloped in fibrous inorganic material such aspotassium titanate paper and compressed so that the active material isforced into the pores of the fibrous sheet. Alternatively, the fibersmay be dispersed throughout the active material. This improvement hasparticular application to high energy density and rechargeable batteriesusing cadmium and nickel or silver. U.S. Pat. No. 3,703,413 discloses amethod of making inorganic fibers, such as zinc oxide fibers, which maybe incorporated into the electrodes of zinc-containing batteries. Noneof these approaches have application to metal acid batteries,particularly lead acid batteries. And, like the approaches summarizedabove, all represent a trade-off between durability, capacity andspecific energy.

Another approach which has been used to decrease the weight of the leadacid battery is to utilize a lead alloy in the electrode. Lead alloyssuch as antimony may be used to give strength to the battery'selectrodes, but such batteries are still relatively heavy and thepresence of the alloy may result in increased corrosion and gassing. Forinstance, although antimony adds strength to the electrode and increasesthe resistance of the grid to shedding of the active material under deepcycling, it is highly susceptible to corrosion and gassing. Further, thepresence of antimony is undesirable because it promotesself-discharging. Calcium alloy is not as susceptible to corrosion, butthe presence of calcium reduces the electrical conductivity of the gridby causing a calcium-based plaque to form around the positive gridconductors. This plaque formation is non-reversible and increases withage and the number of battery charge-discharge cycles, causing a gradualand permanent decrease in battery capacity.

Although all of these approaches have their merits, all represent atrade-off between weight, capacity and durability, and as far as isknown, none have provided the light-weight, longlife battery necessaryto allow the commercialization of such developments as theelectrically-powered automobile on a large scale.

One approach which could provide significant weight reduction withoutimpairment of the capacity and durability of the battery is the coatingof a light-weight, high tensile strength fiber with sufficient lead suchthat the resulting composite wire would be suitable for use in the gridof the electrode. For instance, U.S. Pat. No. 3,808,040, summarizedabove, notes that the method for strengthening a conductive latticeworkdisclosed by that patent may be used on a tissue of lead-coated glassfibers. However, to date, no wire with a coating of lead of sufficientthickness, purity and continuity has been available. As noted above,pure lead wire is not strong enough to use in lead acid batteries, andprevious attempts at coating stronger materials with lead have beenunsuccessful in making a product which may be used in such a battery.For instance, U.S. Pat. No. 275,859 discloses an apparatus for theextrusion of lead onto a core material, in particular, a telegraphcable. However, the apparatus disclosed in that patent is not capable ofdeveloping the high extrusion pressures necessary to extrude lead onto acore material of small enough diameter to be capable of being used forthis purpose. The problem is complicated by the fact that there are fewmaterials with the desired characteristics of high corrosion and hightensile strength, among others, which can survive chemical attack in alead oxide-sulfuric acid battery.

Short fibers composed only of lead are disclosed in U.S. Pat. No.3,466,193, also summarized above. U.S. Pat. No. 3,556,855 discloses theuse of metal-coated fibers in an electrode, but the fibers are of shortlength and are prepared using an electroless plating process, a methodwhich does not provide the thickness and continuity of coating required,particularly in the case of the deposition of a lead coating, to make agrid from such a wire. The patent does disclose the mixing of athermosetting resin with fibers coated by electroless deposition to forma grid element.

U.S. Pat. No. 4,169,911 discloses short, metal-coated carbon fibers heldtogether by a binder for use in battery electrodes, and notes that leadis one of the metals which may be used to coat the fibers. It indicatesthat the fiber may be coated by electrochemical plating, chemicalplating, vacuum deposition, sputtering, ion plating, plasma jetapplication or chemical deposition. However, none of these methods canbe used to produce a lead-coated wire capable of being woven into ascrim which may be used as an electrode grid. The fibers disclosed bythis reference are characterized by a conductivity which is too low, dueto the thinness of the layer of metal deposited on the fiber, for such ause. Nor do the metal-coated fibers produced by such processes possessthe necessary surface characteristics (i.e., uniform, small grain size)to resist corrosion in a lead-acid environment. Further, the strength ofthe porous material disclosed by this reference is too low to supportthe layer of active material of the electrode.

U.S. Pat. No. 3,776,612 discloses short carbon or asbestos fibers platedwith lead for use as a bearing material. Although the conductivity ofthese fibers may be adequate for batteries which are used in certainapplications, the relatively thin plating would be oxidized rapidly inthe harsh environment of the lead acid battery, resulting in brokenelectrical continuity, rendering the battery useless. Further, theprocess disclosed by this reference for the making of such fibers isrelatively slow and expensive.

The electrodeposition of metal, including lead, onto synthetic polymerfibers using a metal chloride nitrate or sulfate solution is disclosedby U.S. Pat. No. 3,940,533. Such fibers show improved conductivity andantistatic properties. Again, the thinness of the lead coating precludesthe use of this material as the grid conductor of a battery. Further,the fibers disclosed would not survive the sulfuric acid and lead oxideattack of the lead acid battery.

U.S. Pat. No. 3,958,066 discloses a method of making synthetic polymerfibers with a metal powder attached to their surface for improvedconductivity and antistatic applications. Such a fiber is useless in alead acid battery because the synthetic polymer would not survive thechemical environment of the battery and because pure lead, not particlesof lead, must form a continuous coating on the fiber in order to avoidrapid oxidation of the lead and to provide the necessary electricalconductivity.

U.S. Pat. No. 2,963,739 discloses an apparatus and method of applyingmetal to glass filaments. Glass fibers are drawn through a bead ofmolten metal which forms at the face of an applicator, then stranded andspooled. The apparatus is apparently intended for the coating of glassfibers with copper, aluminum, silver or alloys of these metals, but is,however, unsatisfactory for coating of lead or zinc onto metal wire orglass fibers. Both melted lead and melted zinc have high surfacetensions and poor wetting characteristics. When those characteristicsare added to the fact that, when melted, both oxidize easily and have apoor affinity for glass, the result is an impure and irregular coatingwhich is unsatisfactory because of the effect of those impurities andirregularities on the electrical conductivity of the coated wire andbecause those impurities and irregularities expose the core of thecomposite wire to the acid of the lead acid battery, resulting in damageto the core. To a lesser extent, this same problem exists with regard tothe coating of a core material with nickel or zinc.

Another approach which can be utilized to reduce the weight of thebattery while improving its electrical characteristics is to make theconductor, or bus bar, which removes current from the grid, and/or whichpasses current from grid to grid within the battery, lighter and toimprove its conductivity so that a proportionally smaller conductor canbe utilized. Those objectives could also be accomplished by providing acomposite wire with a core made of a conductive metal such as copper oraluminum and a thin coating of lead. However, so far as is known, nocomposite wire is available to satisfactorily provide such a reductionin weight or size.

Taking advantage of the fact that only the outermost layer of the leadof the grid element is necessary for proper function of the electrodesof a metal acid battery, the present invention provides a continuousmetal coated, composite wire of small diameter. This wire may be woveninto a scrim in a wide variety of shapes and sizes for use as a gridwhich may be used in an electrode in an electrochemical cell. Such agrid is characterized by the desired properties of strength, durability,corrosion-resistance, conductivity and light weight. It is, therefore,an object of the present invention to provide a lightweight, metalcoated fiber wire of small diameter and continuous length.

It is another object of the present invention to provide a lightweight,lead coated wire with the high tensile and shear strength and corrosionresistance necessary to allow the use of the wire in the electrode of anelectrochemical cell.

It is another object of the present invention to provide an apparatusand method of making a metal-coated wire, the surface of which ischaracterized by extremely high corrosion resistance properties arisingfrom precisely controlled, solid-phase extrusion of the metal coatingonto a core of a fibrous material, optical fiber or highly conductivemetal.

It is another object of the present invention to provide a material fromwhich a grid for an electrochemical battery may be made which willextend the life and reduce the weight of the battery.

It is another object of the present invention to provide a material fromwhich a grid for an electrochemical battery may be made which willincrease the specific energy of the battery.

It is another object of the present invention to provide a method formaking a metal coated fiber.

A further object of the present invention is to provide a method forcoating a fibrous material with an extrudible, corrosion-resistant metalsuch as lead, zinc or nickel.

It is another object of the present invention to provide a method formaking a continuous length of a fine core material with a layer of leaddeposited around the core material.

A further object of the present invention is to provide an apparatus foruse in the coating of a fine, high tensile strength fibrous materialwith an extrudible, corrosion-resistant metal.

It is another object of the present invention to provide an apparatuscapable of depositing a thin layer of lead, zinc, nickel or othercorrosion-resistant metal around a fine core material.

It is another object of the present invention to provide an apparatuscapable of depositing a thin layer of extrudible, corrosion-resistantmetal around a core material, the corrosion-resistance properties of themetal being enhanced due to the uniform, small grain size of the metal.

It is another object of the present invention to provide an apparatuswhich is capable of making continuous lengths of light weight, leadcoated wire of small diameter.

It is another object of the present invention to provide a light-weight,high tensile strength, metal-coated wire of small diameter, the wirehaving high corrosion resistance capabilities due to the uniform, smallgrain size of the surface of the metal.

Still another object of this invention is to provide a light-weight,durable fabric woven from a metal coated fiber.

Another object of the present invention is to provide a fine, hightensile strength, lead-coated wire which may be woven into a scrim foruse in the electrode of a lead acid battery.

Another object of the present invention is to provide a composite wirecomprising a core of a variety of materials, including highly conductivemetals such as copper or aluminum, and a coating of an extrudible,corrosion-resistant metal such as lead, zinc or nickel.

Another object of the present invention is to provide an improvedelectrode grid constructed of a scrim woven from a lightweight, hightensile strength fiber coated with lead and a bus bar constructed from acore of a highly conductive metal such as copper or aluminum and acoating of lead.

Another object of the present invention is to provide electrode grids ofhigh conductivity, light weight and increased durability for use in anelectrochemical battery.

Another object of the present invention is to provide connectors andcell interconnect cabling of high conductivity and light weight for usein an electrochemical battery.

Another object of the present invention is to provide an electrodecomposed of a combination of a fabric woven from a lead coated fiber anda paste of active material for use in a lead acid battery.

Another object of the present invention is to provide an electrochemicalcell which may be assembled into an electrochemical battery that islight in weight, has a long battery life and has a high specific energy.

A further object of the present invention is to provide a method ofmaking an electrode grid of high conductivity, light weight andincreased durability.

Another object of the present invention is to provide a battery in whichthe interplate and intercellular interconnectors are eliminated.

Yet another object of the present invention is to provide a high tensilestrength conductor which will pass high currents but will blow easily inresponse to high transient currents, thereby serving as a fusingmaterial.

Another object of the present invention is to provide a cabled compositewire comprising several individual fine composite wires having either afibrous material core or a highly conductive metal core and a coating ofan extrudible, corrosion-resistant metal such as lead, zinc or nickel,each and all of the composite wires being contained within an extrudedlead sheath.

Another object of the present invention is to provide a light-weightcloth woven from a lead coated, composite wire useful to absorb ionizingand/or electromagnetic radiation or for noise abatement.

Another object of the present invention is to provide a lead coated,composite wire having an optical fiber core for use in shielded fiberoptic communications circuits.

Various other objects of the present invention and the advantages itrepresents will be readily apparent from the following description ofthe drawings of the apparatus of the present invention, in whichexemplary embodiments of the invention are shown, and the description ofthe method of the present invention.

SUMMARY OF THE INVENTION

The present invention is directed to a method and apparatus for coatinga high tensile strength fibrous material, optical fiber or a highlyconductive metal wire with an extrudible, corrosion-resistant metal suchas lead, zinc or nickel, a method of making such a metal-coated wire,and a metal-coated wire of high tensile strength and electricalconductivity made according to that method and with that apparatus. Theapparatus comprises die means for receiving a high tensile strengthcore, a compression chamber in communication with the die means, andmeans for forcing the metal out of the compression chamber and throughthe die means. A cylinder is also provided comprising a compressionchamber with a piston reciprocally mounted therein, the radial clearancebetween the piston and the walls of the compresson chamber beingvirtually zero. In order to achieve this zero radial clearance, spaced,annular lands are provided on the piston between the body of the pistonand the walls of the compression chamber; the piston, the annular landsand the inside walls of the compression chamber defining a space. Alsoprovided is a means communicating with the compression chamber and thespace defined by the piston, the annular lands and the walls of thecompression chamber operable to allow the extrudible,corrosion-resistant metal to be extruded into said space during thecompression stroke of the piston, thereby relieving the high extrusionpressure exerted on said metal and preventing the escape of said metalpast the piston along the walls of the compression chamber.

The apparatus is provided with a die holder assembly comprising a firstdie member with an aperture in it for passage of a fibrous or metalliccore material that is tapered in the direction of movemeent of the corematerial and a second die member with an aperture in it for passage ofthe core material that is tapered in the direction opposite thedirection of movement of the core material. The first and second diemembers are retained by a cylindrical die separator with a portion atboth ends which is larger in diameter than the central portion. The dieholder assembly is provided with means communicating with a source underpressure and means operable to equalize the pressure exerted by theextrudible, corrosion-resistant metal which is forced into the dieseparator around the core material to achieve a coating on the corematerial of uniform thickness.

According to the method of the present invention, an extrudible,corrosion-resistant metal such as lead, zinc or nickel is extrudedthrough a die means and a core material such as a fine aluminum, copper,silver, gold, nickel or tantalum or high tensile strength fibrousmaterial is drawn through the die means as the metal is extruded. Usingthis method, continuous lengths of a metal wire or a fiber such as anaramid, or fiberglass, carbon or optical fiber can be coated with anuniform layer of the extrudible, corrosion-resistant metal.

The present invention is also directed to a scrim which may be wovenfrom the metal coated wire produced by the method and apparatus of thepresent invention, the electrode which may be constructed using such ascrim as a grid element, and the battery which may be constructed frompositive and negative pairs of such electrodes. Also described is acomposite wire comprising a core of a highly conductive metal and acoating of lead, zinc or nickel, an electrode which may be constructedof a scrim woven from the metal coated, composite wire having either afibrous core material or a highly conductive metal core and a bus barcomprised of a highly conductive metal and a coating of lead, zinc ornickel and the electrochemical cell which may be constructed from apositive and negative pair of such electrodes.

The present invention is also directed to a rechargeable lead acidelectrochemical cell having spiral wound positive and negative electrodepairs, the electrodes being constructed using a scrim woven from themetal coated wire produced according to the method of the presentinvention as a grid element. Several of these electrochemical cells maybe assembled into a rechargeable lead acid battery, the electrode pairsbeing connected in series, and the connections may be in the form of busbars constructed of a composite wire comprising a core of a highlyconductive metal and a coating of lead.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of the apparatus of the present invention showingthe mechanism for feeding the metal into the compression cylinder, thedie holder assembly and the portion of the piston which forces the leadinto the space between dies, in longitudinal cross section.

FIG. 2 is a schematic representation of the apparatus of the presentinvention showing the control system plan.

FIG. 3 is a cross-sectional view of the die assembly of the apparatusshown in FIG. 1.

FIG. 4 is an exploded, perspective view of the die assembly of theapparatus shown in FIGS. 1 and 2.

FIG. 5 is an enlarged longitudinal cross section of the piston whichforces the metal out of the compression chamber and into the spacebetween dies.

FIG. 6 is an elevated, perspective view of a positive electrode whichmay be constructed from a scrim woven with the lead coated wire producedaccording to the method and with the apparatus of the present invention.

FIG. 7 is an elevated, perspective view of an electrode which may beconstructed from a scrim woven with the lead coated wire producedaccording to the method and with the apparatus of the present inventionfor use in the construction of a biplate battery.

FIG. 8 is an elevated, perspective view of an alternative form of theelectrode shown in FIG. 7.

FIG. 9 is a cross section of a biplate battery constructed according tothe present invention taken along the lines 9--9 in FIG. 10.

FIG. 10 is a longitudinal cross section of a biplate battery constructedaccording to the present invention taken along the lines 10--10 in FIG.9.

FIG. 11 is a cross-sectional view of an alternative embodiment of thedie assembly shown in FIG. 3.

FIG. 12 is an exploded, perspective view, of the die assembly of FIG.11.

FIG. 13 is a longitudinal cross section of an alternative constructionof the biplate battery shown in FIG. 10.

FIG. 14 is a front view of an electrode grid constructed according tothe method and with the apparatus of the present invention.

FIG. 15 is an alternative embodiment of the electrode grid of FIG. 14.

FIGS. 16-18 are also alternative embodiments of the electrode grid ofFIG. 14.

FIG. 19 is a top view of a positive and negative electrode pairconstructed according to the method and with the apparatus of thepresent invention, insulated from each other by a separator, as they areassembled into a spiral wound rechargeable lead acid battery.

FIG. 20 is a top view of the positive and negative electrode pair shownin FIG. 19, but showing a different way to wind the positive andnegative electrode pair.

FIG. 21 is a perspective, somewhat schematic, view of a nine volt,rechargeable battery which may be constructed from four of theelectrochemical cells shown in FIG. 22, the case of the battery beingshown in shadow lines to make its interior construction clear.

FIG. 22 is an exploded, perspective view of an electrochemical cellwhich may be constructed from the positive and negative electrode pairshown in FIG. 19.

FIG. 23 is a perspective view of a cabled, composite wire which may beconstructed according to the present invention, with one end of the wirebeing shown cut in cross section and the other end broken away.

DETAILED DESCRIPTION

When used herein, the term "extrudible, corrosion-resistant metal"refers to those metals which are capable of being extruded onto a corematerial using the method and apparatus of the present invention attemperatures below the melting points of those metals. Although othermetals may be known to those skilled in the art who have the benefit ofthis disclosure, the presently preferred extrudible, corrosion-resistantmetals are lead, zinc and nickel, with lead being the most preferred.

The term "core material", as used throughout the specification andclaims, refers to fibrous and metallic materials. The fibrous materialsmay be glass, synthetic, optical or carbon fibers. The glass fibers maybe any one of a variety of commercially available fiberglass fibers, andthe synthetic fibers may be an aramid or other commercially availablesynthetic fiber. The optical fibers may be any of a number ofproprietary glass fiber formulations used for conduction of light pulsesin telecommunications. The metallic materials which are used as corematerials are those highly conductive metals such as aluminum, copper,silver, gold, nickel or tantalum.

In FIG. 1, a preferred embodiment of the apparatus of the presentinvention is shown. Pure extrudible, corrosion-resistant metal such asthe lead balls 10 is loaded into the vibratory feeder 12 for feedingthrough the chute or conduit 14 into the chamber 16 formed by a bore 17through plunger 22 and the upper surface 19 of slide 21. The lead balls10 in conduit 14 are heated to a predetermined temperature by preheatingcoil 18, controlled by thermocouple 20. Plunger 22, connected to thereciprocating feed cylinder 24 by means of the piston rod 26, isinitially in its retracted position, allowing a plurality of heated leadballs 10 to drop into the chamber 16. When activated, feed cylinder 24reciprocates the plunger 22 to move the lead balls 10 retained withinchamber 16 along the upper surface 19 of slide 21 over the aperture 28in the top of compression chamber 30. Feed cylinder 24 is air powered byair input line 32 and output line 34. The cylinder could also behydraulically powered or connected to an electrical solenoid.

When the plunger 22 reaches the position shown in dotted lines 36, theend of the plunger 38 contacts limit switch 40, stopping plunger 22 andreversing the direction of its travel, returning it to its initialposition. In the moment while the plunger 22 is in the position shown bydotted lines 36, the chamber 16 is positioned over the aperture 28 inthe top of the compression chamber 30, allowing the lead balls in thechamber 16 to drop through aperture 28 into compression chamber 30. Whenthe plunger 22 returns to its original position, the corner 42 ofplunger 22 contacts limit switch 44, stopping the travel of the plunger22 and reversing it for another stroke.

In the compression chamber 30, the lead or other extrudible,corrosion-resistant metal may be heated by heat imparted to the walls ofthe compression chamber 46 by the heating coil 48 under control ofthermocouple 49. Once the metal is heated to a predeterminedtemperature, the hydraulic cylinder 50 is actuated, causing piston 52 todescend from its initial position down into the compression chamber 30through aperture 28, forcing the metal out of the chamber throughaperture 54 and into the space 56 between the entry die 58 and the exitdie 60, held in place by die holder 62, and shown in more detail in FIG.3. Die holder 62 is threaded into threaded aperture 121 in the walls 46of the compression chamber 30.

The hydraulic cylinder 50 is actuated by fluid pressure developedthrough input line 64 and output line 66. The lines 64 and 66 areprovided with a proportional control valve 68 and a pressure gauge 70.Hydraulic fluid is pumped from the reservoir 72 by pump 74, through oilcooling radiator 76 to the proportional control valve 68. When thepiston 52 reaches the position shown in dotted lines 78, best shown inFIG. 2, collar 80 contacts limit switch 82, stopping the piston 52,reversing the direction of its travel and returning it to its originalposition. When piston 52 reaches its original position, collar 80contacts limit switch 84, stopping the travel of the piston 52 andreversing it for another stroke.

Compression of the metal by the piston 52 inside the compression chamber30 generates heat. Thermocouple 49 senses the temperature in thecompression chamber 30 and regulates the heating of the walls 46 of thecompression chamber 30 by the heating coil 48.

Core material 86, which may be "E glass" or "C glass" type fiberglass orother suitable fiber such as an optical, carbon or synthetic fiber, or afine wire comprised of a highly conductive metal such as copper oraluminum, may be maintained at a predetermined tension as it is pulledoff the reel 88 by a constant tension motor-control assembly such asthat shown schematically in FIGS. 1 and 2 at 90. As core material 86 ispulled off the reel 88, the shield 92 around the reel 88 helps preventcore material 86 from tangling and shields it from any loose objectsthat may bee near the reel 88. Core material 86 is pulled off the reel88 through a centering ring 94, and drag tension is supplied by springtensioner 96 to prevent fiber tangling. Roller 98 guides core material86 toward the entry die 58 and exit die 60, where it is coated withmetal to form a fine, composite wire 100. As the wire 100 exits from thedie holder 62, it traverses roller 102, turning it downward to traversefloating weight 104, which turns it back up to roller 106, therebyhelping to maintain constant tension during starting and stopping of themotors 90 and 108. The term "wire" is used, with reference numeral 100,to desigdnate the composite wire which results from the coating of corematerial 86, whether it is a fibrous material or a highly conductivemetal wire, with an extrudibdle, corrosion-resistant metal such as lead,zinc or nickel. Roller 110 then guides the wire 100 towards thetraversing means 112. As the wire 100 traverses roller 110, proportionalvelocity encoder 114 measures its speed and cooperates with traversingmeans 112 and motors 90 and 108 to wind the wire 100 onto the take-upspool 116. The traversing means 112 moves back and forth along thetraverse bar 118 to insure even winding of the wire 100 onto the take-upspool 116.

Referring now to FIGS. 3 and 4, entry die 58 and exit die 60 areretained within die separator 120 by spacing washers 122a and 122b. Dieseparator 120 is retained within the cavity 65 in the die holder 62, andcompression is provided by the tightening of the retaining plug 124 inthe threads 123 in the die holder 62. Entry die 58 is provided withflange 59 and exit die 60 is provided with flange 61, the flanges 59 and61 abutting the ends 119 of the die separator 120, thereby maintainingthe spacing between the dies in the interior 56 of the die separator120. Die holder 62 is provided with an aperture 126 which, when the dieseparator 120, entry die 58, exit die 60, and spacing washers 122 areassembled into the die holder 62, will be aligned with the aperture 128in the die separator 120. Aperture 126 is sized to fit snugly againstaperture 54 on the bottom of the compression cylinder 30 when die holder62 is screwed on threads 119 into the threaded aperture 121 in the wall46 of the compression cylinder 30.

Die holder 62 is also provided with aperture 130 for passage of corematerial 86 (not shown). Entry die 58 is provided with an aperture 132at the apex of the taper 134. Metal is forced out of compression chamber30 by piston 52, through apertures 54, 126 and 128, and into the space56 between the entry die 58 and exit die 60.

The exit die 60 is provided with an exit aperture 136 at the apex of theconical taper 138. The taper 134 of entry die 58 is tapered in thedirection of the movement of the core material 86. The taper 138 of exitdie 60 is preferably tapered in the direction opposite the direction ofmovement of core materials 86, but can be tapered in the same directionas the movement of core material 86, or not tapered at all. Tapering theexit die 60 in the direction opposite the direction of movement of corematerial 86 is preferred because, even though other configurations mayallow the use of decreased extrusion pressures, the tooling life andconcentricity of the core material 86 in composite wire 100 suffers.Further, retaining plug 124 must be torqued more tightly into threads123 against the washers 122 and flanges 59 and 61 of entry die 58 andexit die 60, respectively, because of the increased pressure exertedagainst the exit die 60 by the metal in space 56, if the exit die 60utilized is not tapered in the direction opposite the direction ofmovement of core material 86. Retaining plug 124 is also provided withaperture 149 for passage of wire 100.

Referring to FIGS. 11 and 12, there is shown a presently preferredembodiment of the die assembly of FIGS. 3 and 4 in which the variouscomponents are, to the extent possible, given reference numerals anddescriptive names corresponding to those of the components shown inFIGS. 3 and 4. In particular, the entry die 58' and exit die 60' areretained within die separator 120' by back-up washers 122a' and 122b',and compression is provided by the tightening of the retaining plug 124'into the cavity 65' in the die holder 62' on the threads 123'. Becausethe retaining plug 124' is provided with threads 125' on which it isthreaded into cavity 65' in die holder 62', it may have a slight cant tothe face 63', which could result in the shewing of the exit die 60'within the die separator 120'. To prevent any such skewing, a thrustwasher assembly having a convex face washer 67' and a concave facewasher 69' is interposed between the retaining plug 124' and the back-upwasher 122b'. The interaction of the concave and convex surfaces ofwashers 67' and 69' effectively prevents any skewing which may resultfrom the tightening of retaining plug 124' against back-up washer 122a'.

The die holder 62' is provided with aperture 126' which is sized to fitsnugly against the aperture 54 on the bottom of compression cylinder 30'(see FIGS. 1 and 2). Die separator 120' is provided with flanges 127a'and 127b' at each end, and a central portion 129' of smaller diameter,the diameter of flanges 127a' and 127b' being approximately the same asthe inside diameter of the cavity 65' in the die holder 62' whichreceives die separator 120'. The combination of flanges 127a' and 127b'and the smaller diameter of the central portion 129' of die separator120' leaves a space 131' between the central portion 129' of dieseparator 120' and the inside wall of cavity 65' in die holder 62'.Space 131' is in fluid communication with the interior 56' of dieseparator 120' by means of apertures 135a' and 135b'.

Because of the pressure exerted by the pressurized material in space 56'against the entry die 58' and exit die 60', there is no need for flangeson the dies 58' and 60' such as the flanges 59 and 60 shown in FIGS. 3and 4. In order to retain the dies within the space 56' in die separator120' during transmit, and to insure the axial alignment of the dies, thediameter of the dies is approximately 0.0005 inches larger than thediameter of the inside walls of the interior 56' of die separator 120and the dies are pressed fit into die separator 120' using heat, oil anda hydraulic press.

Die holder 62' is also provided with aperture 130' for passage of corematerial 86 (not shown). Entry die 58' is provided with an aperture 132'at the apex of the taper 134'. Exit die 60' is provided with an exitaperture 136' at the apex of the conical taper 138'. Retaining plug 124'is also provided with aperture 140' for passage of wire 100.

The embodiment shown in FIGS. 11 and 12 is characterized by the factthat the pressure exerted on core material 86 as it passes through space56 is equal in all directions. When producing small diameter compositewire with an apparatus such as is shown in FIGS. 3 and 4, the corematerial does not stay centered within the space 56 relative to theaperture 136 in exit die 60 as a result of the differential pressureexerted on core material 86 from above as the lead is forced throughapertures 126 and 128. This differential pressure forces core material86 downwardly such that it no longer enters the aperture 136 in the exitdie 60 in the center of that aperture 136, causing the core material 86to be off-center in the composite wire 100. This differential downwardpressure may also be sufficient to cause the deformation of the toolingin the die carrier 62.

The high extrusion pressure is the result of the economy afforded byhigh production speeds. To maximize production efficiency and reduce theneed to reload the compression chamber, a larger diameter compressionchamber 30 (approximately 0.625 inches) and piston 52 are used. A smalldiameter chamber and piston would require frequent stopping of theapparatus for reloading. However, when producing a 0.015 inch diametercomposite wire with a 0.010 inch glass core, the large diameter of thechamber and piston causes the reduction ratio to exceed 3100 to 1. Theuse of a compression chamber of very long length and small diameterwould result in less frequent reloading and a decrease in reductionratio, but is not preferred because of the problems of alignment of thepiston and compression chamber and the lack of stiffness in a longpiston.

This high pressure is also a result of the mathematical fact thatextrusion pressure is not a linear function of the reduction ratio,consequently extrusion pressure increases at a rate greater than theproportional increase in the reduction ratio. High extrusion pressurescreate design problems which are overcome in the present invention. Forinstance, it is known that when reduction ratio exceeds 250:1, theextrusion pressure will be so high that it will exceed the capability ofthe walls of the compression chamber to retain their shape even if thewalls are constructed of high strength steel. Such high extrusionpressures can actually cause the walls of the chamber to bow outwardlyas the piston is urged against the metal in the chamber, allowing themetal to escape past the piston, creating the problems which result fromsuch leakage that are discussed below. The bowing of the cylinder wallsis particularly pronounced when the piston is approximately half waydown the cylinder. To prevent this bowing of the walls of thecompression chamber, multiple concentric cylinders (not shown) are usedas the walls of the compression chamber. In a presently preferredembodiment, as many as four cylinders, the outside diameter of eachbeing approximately 0.001 inches larger than the inside diameter of theadjacent, surrounding cylinder, are pressed one into the other to formthe walls of the compression chamber.

To minimize the loss of this extremely high extrusion pressure, therebyavoiding the use of even higher pressures to achieve the desiredpressure in the space 56, the exit die 60 is placed directly beneath thecompression chamber 30, resulting in the differential pressure acrossthe apertures 126 and 128 and the deflection of the core material 86downwardly in space 56. To minimize this differential pressure, whilestill minimizing the extrusion pressure required, the presentlypreferred construction of FIG. 11 is utilized. Exit die 60' is locateddirectly below compression chamber 30, but metal is admitted into thespace 56 in two directions which are 180 degrees apart, therebyequalizing the pressure exerted against the core material 86. Materialis forced out of compression chamber 30 by piston 52, through apertures54 and 126', into the space 131', around the central portion 129' of dieseparator 120', through apertures 135a' and 135b', and into the space56' between entry die 58' and exit die 60'. Additional apertures may beprovided so long as they are spaced at regular intervals around thecentral portion of die separator 129' and so long as none of theapertures is located directly under the aperture 54 at the bottom of thecompression chamber 30. Using the embodiment shown in FIGS. 11 and 12,the concentricity of the core material relative to the outside diameterof the composite wire 100 can be maintained to within ±5%.

Piston 52 is shown in enlarged detail in FIG. 5. The piston 52 isprovided with a beveled surface 142 on the bottom of the piston 52. Thepiston 52 is also provided with annular lands 144 and 146, and atransverse hole 148 through the piston. Vertical hole 150 communicateswith transverse hole 148. Beveled surface 142, lands 144 and 146,transverse hole 148 and vertical hole 150 cooperate to help seal piston52 along the inside wall 152 (FIG. 1) of compression chamber 30 and tohelp center the piston 52 in the compression chamber 30 during thecompression stroke of piston 52. Metal under high pressure is forced upthrough vertical hole 150 into transverse hole 148 and into the spaceformed by lands 144 and 146 and the inside wall 152 of the compressionchamber 30 effectively sealing piston 52 against the wall 152 andcentering it within the compression chamber 30.

This sealing construction is made necessary by the high extrusionpressure of the appartus. For instance, even though the clearancebetween the piston 52 and the inside wall 152 of compression chamber 30can be made as small as 0.0005 inches, that much radial clearance isenough to allow excessive leakage of the extrudible, corrosion-resistantmetal past piston 52 during compression, and the concommitant loss ofusable extrusion pressure. Because of the small diameters of thecomposite wires which may be produced using the method and apparatus ofthe present invention, if this sealing construction is not used, as muchas ten times more metal can leak past the piston 52 than is applied tothe core material. In addition to the fact that this leakage results inthe use of more metal (although the leakage can be recycled) andtherefore requires more frequent reloading of compression chamber 30,thereby slowing production, this leakage is generally asymmetrical,causing the piston 52 to be pushed off center in compression chamber 30and into contact with the wall 152. This contact results in theimmediate scoring of the walls 46, causing even greater leakage and lossof extrusion pressure. It is for this reason that the extremely long,small diameter compression chamber discussed above has proved to be oflittle aid in overcoming the need for frequent reloading of the chamber:the alignment and rigidity problems associated with such a constructionmultiply the problems of centering the piston in the chamber, therebyexacerbating the leakage of metal past the piston. In addition to thedamage caused, the increased leakage and decreased extrusion pressurecauses a drop in the maximum production rate, all of which arelimitations which make the sealing construction of the piston 52 acentral feature of the apparatus of the present invention.

The construction shown in FIG. 5 allows the extrudible,corrosion-resistant metal to flow into the space formed by piston 52,lands 144 and 146, and the inside wall 152 of compression chamber 30.The metal which extrudes into this space lacks the pressure needed toextrude past annular land 144, effectively preventing leakage pastpiston 52.

Additionally, the metal which extrudes into the space formed by piston52, lands 142 and 144, and wall 152 is, depending on the extrusionpressure, pressurized to between about 5,000 and 10,000 PSI. Generally,it appears that the pressure of the metal in this space will vary fromapproximately one fourth to one third of the pressure of the compressionchamber 30. This pressure is exerted between piston 52 and wall 152equally around the piston 52, forcing piston 52 to the center ofcompression chamber 30 and further preventing contact between the piston52 and wall 152. At the same time, the metal in this space provides whatamounts to a low friction bearing surface which is similar to a babbitbearing, reducing piston drag and leaving more hydraulic force forextrusion. Pistons with seals constructed in this manner have beentested for several months. After millions of cycles, no sign of wear orleakage has appeared, and the piston and cylinder wall are unscored evenafter heavy use, all of the extrudible, corrosion-resistant metal havingbeen applied to the core material.

The use of a long, small diameter compression chamber would most likelyobviate the need for the sealing construction of piston 52 since thesmall diameter of the chamber 30 would reduce the reduction ratio to apoint at which it would not develop the 40-50,000 PSI extrusionpressures required by the preferred embodiment of the present inventionto maintain efficient production rates. In fact, the use of a long,small diameter compression chamber has such an effect on extrusionpressure that it would likely permit the use of a straight pistonwithout any seals. However, the aforementioned alignment, stiffness andcentering problems associated with such a construction are such seriouslimitations as to limit the utility of that construction.

Hydraulic cylinder 50 is mounted on platform 154, supported above base158 by columns 156, and held in place by bolts 160 and 162. Slide 21 ismounted to columns 156 and serves as a support for feed cylinder 24 andits piston rod 26 and plunger 22. Compression chamber 30 is supported bytable 164 and is provided with a downwardly projecting hemispherical ear166 which is received within cavity 168 of table 164. Bolt 170 projectsup through a hole 172 in the base 158 and hole 174 in table 164 and isreceived in the threaded aperture 176 of the hemispherical ear 166. Theinside radius of cavity 168 is slightly larger than the radius ofhemispherical ear 166 such that when compression chamber 30 is screwedonto bolt 170, cavity 168 and hemispherical ear 166 will cooperate tocenter the compression chamber on table 164 so that aperture 28 is inaxial alignment with bore 17 when plunger 22 is in the extended positionshown by the dotted lines 36 in FIG. 1 and in axial alignment withpiston 52 when plunger 22 returns to its initial position.

Referring now to FIG. 2, operation of the apparatus of the presentinvention is controlled from control panel 178 by appropriate circuitry.Control panel 178 is connected to feed cylinder 24 by input line 32 andoutput line 34. Proportional control valve 68 is connected to thecontrol panel 178 by input line 68_(i) and output line 68_(o), therebycontrolling hydraulic cylinder 50. Limit switches 40, 44, 82, and 84 andmotors 90 and 108 are connected to control panel 178 by the respectiveinput and output lines 40_(i) and 40_(o), 44_(i) and 44_(o), 82_(i) and82_(o), 84_(i) and 84_(o), and 108_(i) and 108_(o), and 90_(i) and90_(o). Inputs to the control panel 178 are received from thethermocouples 20 and 49 through lines 20_(i) and 49_(i), respectively,and preheating coil 18 and heating coil 48 are controlled on the basisof that input through respective input and output lines 18_(i) and18_(o) and 48_(i) and 48_(o). Input is also received from proportionalvelocity encoder 114 by means of line 114_(i). In this manner, alloperational parameters may be set and controlled before and/or duringoperation of the apparatus of the present invention.

An important characteristic of the continuous, composite wire of thepresent invention is its resistance to corrosion from attack by the acidof a battery or, in the case of fiber optic communications cables, theharsh environment in which the cable will be used as described below. Asa general rule, the smaller the grain size of lead, for instance, thegreater its resistance to corrosion. The large grain size does notitself cause corrosion, but when corrosion starts, it attacks the grainboundaries, and small grain size reduces the susceptibility of the grainboundaries to attack. The method and apparatus of the present inventionresult in the extrusion of lead of high corrosion resistance at leastpartly because of the small grain size produced.

When lead is cast and then solidified, the average grain size isapproximately 0.25 inches. Using the method and apparatus of the presentinvention, the average grain size of the lead is approximately 0.25×10⁻⁶inches as determined with the scanning electron microscope.

The method of the present invention may be better understood byreference to the following examples.

EXAMPLE I

For use in Example I, the apparatus of the present invention wasprovided with an entry die with an aperture of approximately 0.013". Theaperture in the exit die was approximately 0.020" in diameter, and thedistance between the end of the entry die and entrance of the exit diewas set at approximately 0.006".

Lead balls were loaded into vibratory feeder, vibrated into the conduitfor preheating, and then allowed to feed into the compression chamber,where the lead was heated further and the temperature in the chamberallowed to stabilize at approximately 450° F. With the constant tensionmotor-control assembly pulling the fiber to keep it from tangling, thefiber was moved through the dies at a rate of approximately 100 feet perminute while the lead was extruded at a pressure of approximately 40,000pounds per square inch (PSI), plus or minus 25%. When measured at theapex of the exit die aperture, the temperature of the lead wasapproximately 585° F.

Using this method, a commercially available aramid fiber, marketed underthe trade name "KEVLAR 49", was used as a core fiber to produce a fine,continuous, composite, electrically conductive wire of a diameter ofapproximately 20 mils. The thickness of the lead around the fiber corewas approximately 5 mils.

EXAMPLE II

The same operating procedure was used to coat a commercially availablechemical glass yarn known in the industry as "C glass". Production ratesof from 150 to 300 feet per minute were utilized at extrusion pressuresof 40,000 to 50,000 PSI, plus or minus 25%. When "C glass" is used asthe fiber core of a lead coated wire, the composite wire producedaccording to this procedure has a diameter of approximately 0.025 inchesand the thickness of the lead coating is approximately 0.006 inches.

EXAMPLE III

The same operating procedure was used to coat a commercially available Cglass of 0.010 inches in diameter, resulting in a composite wire with anoutside diameter of 0.015 inches. An entry die with an aperture ofapproximately 0.012 inches in diameter was used with an exit die with anaperture of about 0.015 inches, and the space between the dies was about0.003 inches. Extrusion pressures of from about 40,000 to about50,000±25% PSI were utilized.

EXAMPLE IV

The same operating procedure was used to coat a 24 AWG copper wire witha diameter of 0.20 inches with lead, resulting in a composite wire witha diameter of 0.028 inches. The diameters of the entry and exit diesutilized were about 0.021 and about 0.028 inches, respectively, and thespace between the dies was about 0.004 inches. Extrusion pressures offrom about 30,000 to about 40,000 PSI±25% were utilized.

EXAMPLE V

The same operating procedure was used to coat an aluminum wire 0.008inches in diameter with lead, resulting in a composite wire with adiameter of 0.015 inches. The diameters of the entry and exit diesutilized were about 0.010 and about 0.015 inches, respectively, and thespace between the dies was about 0.003 inches. Extrusion pressures offrom about 40,000 to about 50,000 PSI±25% were utilized.

EXAMPLE VI

The same operating procedure was used to coat a single monafilamentoptical fiber available from Owens-Corning Fiberglass of 0.015 inches indiameter with lead, resulting in a composite wire with a diameter of0.025 inches. The diameters of the entry and exit dies utilized wereabout 0.018 and about 0.025 inches, respectively, and the space betweenthe dies was about 0.005 inches. Extrusion pressures of from about30,000 to about 40,000 PSI±25% were utilized.

Similar operating parameters may be used to coat other fibers withextrudible, corrosion-resistant metals such as lead, zinc or nickel. Forinstance, other grades of Kevlar may be used, as well as materials suchas the carbon fibers which are commercially available under the tradename "FORTAFIL" made and sold by the Great Lakes Carbon Corporation inNew York in several grades. In addition, other glass yarns such as theyarn known as "E glass" may be coated using the method of the presentinvention. Highly conductive metals such as silver, gold, nickel andtantalum may likewise be suitable as core materials for the compositewire of the present invention.

Production rates as high as about 500 feet per minute have been attainedwith the apparatus and method of the present invention, with extrusionpressures ranging up to about 60,000 pounds per square inch. The speedat which the composite wire is produced is limited by the temperature ofthe metal at the aperture of the exit die. This temperature will varyaccording to the metal being coated onto the core material and thepressure at which it is extruded. For instance, under the conditionssummarized in Example I above, the temperature of the metal at theaperture of the exit die is approximately 585° F. This temperature issignificantly lower than the melting point of lead, 620° F., therebypreventing liquid lead runaway, yet high enough to impart the requiredplasticity to the lead. In the case of zinc or nickel, temperatures atthis point of between 725° and 760° F. or 1950° and 2050° F.,respectively, are called for. Generally, at higher production rates,higher extrusion pressures are required, and hence, the temperature atthe aperture of the exit die will be higher. In order to attainproduction rates higher than about 500 feet per minute under theconditions summarized in Example I, above, it is necessary to cool thearea around the dies, i.e., by the use of hydraulic oil or syntheticcooling fluid such as is available under the brand name DOWTHERM, or asimilar fluid, and input and output lines leading to a heat radiator.

The composite wire having a core of either a fibrous material or ahighly conductive metal made by the above-described methods and acoating of lead may be woven on a conventional weaving apparatus into ascrim or wire cloth. In addition to its use in electrochemical cells,such a scrim or cloth has a number of other uses, for instance, as ablanket or wrapping to absorb ionizing and/or electromagnetic radiationor as sound insulation. The mass of the scrim per unit area, and henceits ability to absorb ionizing radiation, is governed by the number anddiameter of composite wires per unit of length of the woven cloth, andto a lesser extent, by the choice of core material. Of course, a fabricwoven from the composite wire of the present invention will not havetotal shielding, but will significantly attenuate the radiation.Multiple layers may also be used to increase attenuation as desired.

A large scrim or blanket woven with a lead-coated E glass core 0.020inches in diameter, the core being 0.013 inches in diameter, can, forinstance, be woven 10 strands to the inch and supplied in rolls. Theblanket is wound off the rolls and glued or expoxied to the sheetrockused to finish out the interior walls of a building, thereby providingeffective shielding of that room so that it can be safely used for X-rayequipment or radiation therapy equipment. The blanket may also be usedas a curtain, hung, for instance, from a track so that it can beretracted for the same purpose.

When an optical fiber is used as the core material, the resultingcomposite wire has particular application in telecommunications cables.Several such composite wires may be cabled and coated with a lead sheathas shown in FIG. 23 and as will be developed. Optical telecommunicationscables are often laid through sewers, buried in the earth, or placed inother environments in which the cable will be subject to chemical attackeither directly or from the products of certain types of bacteria foundin such locations. In such environments, conventional insulating andprotectant coatings may be degraded, whereas a coating of lead or otherextrudible, corrosion-resistant metal will not be degraded.

The presently preferred use of the composite wire of the presentinvention is as a grid in the electrode of a lead acid battery, shown inFIG. 6. The scrim 180 is cut to the appropriate size and a pure (oralloyed) lead back frame 182 is provided to collect and remove currentfrom the grid. For special applications, at the points in the fabric atwhich the lead wires cross each other 184, the wires may be welded orelectroplated together. At the edges of the scrim, the wires may eitherbe wrapped, as shown at 186, or provided with a frame 182, as shown at188. The frame 182 may be cast, welded, or extruded onto the scrim 180,and may be comprised of any appropriate material providing mechanicalstrength, with or without electrical properties.

The scrim of composite wire, having either a fibrous material or ahighly conductive metal core, may also be provided with a frameconstructed of a composite wire, or bus bar, constructed according tothe present invention and having a highly conductive metal core as shownin FIG. 14. For purposes of clarity, the details of the electrode gridwhich are shown in FIG. 6 are not shown in FIG. 14 (or FIGS. 15-18).FIG. 14 shows a grid constructed of a scrim 195 and frame 196, the frame196 terminating in two posts, designated generally at 197, which are,electrically speaking, integral in that both carry current of the samecharge in the same direction, i.e., to the terminal of a battery (notshown) or to another grid in the battery (not shown). The ends of thewires which comprise scrim 195 are soldered to frame 196. The frame iscomprised of a relatively thick composite wire (i.e., 0.028 inches indiameter in a presently preferred embodiment) having a copper corematerial and a lead coating in a presently preferred embodiment. Thisconstruction combines the high conductivity of copper with the long lifeprovided by the fact that the acid in the battery "sees" only theexterior coating of lead on the bus bar or frame 196. For specialapplications in which the weight of the battery is not of primaryconcern, or in which a high current is needed, or in situations in whichthe normal heating of the battery during charge/discharge cycles must beminimized, the scrim 195 may also be constructed of a composite wirehaving a highly conductive metal core rather than a fibrous materialcore. Depending upon the use to which it will be put, severalalternative constructions of the bus bar and scrim may be utilized suchas those shown in FIGS. 15-18.

When a composite wire made by extruding a 0.006 inch coating of leadonto C glass with a 0.013 inch diameter was woven into such a scrim, theweave was such that the distance between the points 184--184 in FIG. 6was approximately 0.2 inches. It will be recognized by those skilled inthe art who have the benefit of this disclosure that spacings as largeas about one inch or as small as about 0.1 inches may be desirable incertain applications, and that different diameters of lead-coated wiremay be woven into a scrim to optimize grid strength and conductivity forcertain applications. For instance, negative grids have differentoperating requirements, and may require different scrim spacing and leadcoating thickness than positive grids.

The grid shown in FIG. 6 may be used for either the positive or negativegrid of the battery. When used as the positive grid, the scrim 180 mustbe coated with a thick layer of active material. Because of the looseweave of the scrim 180, during manufacture of the positive electrode, apaste of active material 190 may be forced into the spaces 192 of thescrim 180. When cured, the latticework of the scrim acts as ascaffolding to retain the active material on the grid, and the result isan electrode of increased durability and conductivity, and decreasedweight. Further, the tests which are described below have shown that itis possible to modify batteries according to the teachings of thepresent invention such that the modified battery will out-perform anidentical, unmodified battery. Consequently, it has been discovered thatit is possible to reduce the amount of active material applied to eachgrid, while maintaining the performance characteristics of the batteryconstructed from those grids, resulting in a savings of space as well asweight.

For even greater durability of the active material of the positiveelectrode, with decreased weight compared to conventional positiveelectrodes, lead-coated composite wire made according to the method ofthe present invention of approximately 0.015 inches in diameter with alead coating of approximately 0.003 inches in thickness may be choppedinto short pieces (approximately 0.1 to 0.5 inches long) andhomogeneously mixed into the paste of active material. As shown in FIG.6, the short pieces of lead-coated composite wire 194 are dispersedthroughout the paste of active material 190, and the paste is thenapplied to the scrim 180. The high tensile strength of the lead-coatedcomposite wire in the scrim 180 helps hold the active material in placein much the same manner that steel reinforcing bars give strength toconcrete castings, and the pure lead coating of the short lead-coatedcomposite wires 194 provides a multitude of light weight,superconducting paths through the active material 190. In this manner,the electrode constructed in accordance with the present inventionovercomes the limitations of the thickness of the active materialimposed by the weight of the active material, the semiconductorcharacteristics of the active material and the internal support neededto keep the active material from falling apart.

Even though the layer of active material on the negative electrode gridis strong enough and of adequate electrical conductivity so as not torequire the presence of the chopped lead-coated composite wire asdescribed above, the composite wire of the present invention may stillbe used to advantage in the negative electrode. In particular,lead-coated composite wire produced according to the method of thepresent invention may be woven into a scrim to serve as the grid elementof the negative electrode. Because of the high tensile and shearstrength of the composite wire of the present invention and its lightweight, such a grid represents a significant improvement in thedurability of the grid as well as a substantial decrease in the weightof the grid.

A plurality of pairs of positive and negative electrodes constructedaccording to the present invention may be assembled into an otherwiseconventional battery case to provide a battery of high capacity, longlife and high specific energy.

The lead-coated composite wire of the present invention is particularlywell adapted for use in a so-called "biplate" battery. These batteriesare characterized by the high voltages they produce (on the order of 2.2V per cell and 50-150 VDC per battery), with low current, and theirsmall size, which can be as small as that of a conventional battery. Ofspecial significance is the fact that each of the cells of a biplatebattery conducts energy "through the wall" of the cell and into the nextcell, eliminating the heavy lead bus bars that parallel the positivesand negatives in a single cell. Further, since battery output current islow and voltage is high, smaller lead posts can be used at each of endof the battery, leading to further weight savings.

A biplate battery can be constructed of a series of cells arranged so asto keep the electrolyte of each of the cells separate while providingfor electrical continuity between cells. This separation is accomplishedby plates 198 (See FIGS. 7-10), made of polyethylene, polypropylene orsimilar material, the edges 200 of which are embedded in the walls 202of the battery case 204, sealing the cells 206A, 206B, 206C, and 206D.The top edges 208 of the plates 198 are embedded in the top 210 of thebattery case 204 to completely seal the cells 206A, 206B, 206C, and206D.

The electrical conductivity between cells is provided by the lead-coatedwire of the present invention, which is woven into a scrim 212 andwrapped around the edges of the plates 198 before the plates 198 areembedded in the walls 202 and top 210 of battery case 204. The scrim 212can be woven and applied to the plate 198 in the configuration shown inFIGS. 7 and 10, which is the presently preferred configuration, or inthe alternative embodiment shown in FIG. 8. In the embodiment shown inFIGS. 7 and 10, the current moves from cell 206D to cell 206C, and thenon to cell 206B and cell 206A, in the direction of the arrows 214 (i.e.,over the top 208 of plate 198). In the alternative embodiment shown inFIG. 8, the current moves from one cell to the next in the direction ofarrows 216 (i.e., around the edges 200 of plate 198). It is understoodthat a combination of a tight press fit and/or sealant is used at theedges 200 and top 208 of the plates 198 to seal them to the walls 202and top 210 of battery case 204 regardless of which embodiment is used.

If the embodiment shown in FIGS. 7 and 10 is utilized, the number ofvertical wires in the scrim 212 is increased to facilitate conductanceover the top edge 208 of plate 198 in the direction of the arrows 214;if the embodiment shown in FIG. 8 is utilized, the number of horizontalwires in the scrim 212 is increased to facilitate conductance around theedges 200 of the plate 198 in the direction of the arrows 216. Theplates 198, with the scrim 212, are provided with a paste of activematerial (not shown for purposes of clarity) as is known in the art. Itis understood that the positive side of each plate 198 is provided witha positive paste, that the negative side of the plate is provided with anegative paste, and that the paste is not continuous around the edges200 or top 208 of the plates 198. The scrim 212A is provided with alayer of positive paste, and the scrim 212D is provided with a layer ofnegative paste. Depending upon the thickness of the layer of activematerial and the purpose for which the battery will be used, the numberof horizontal wires in the scrim 212 in the embodiment shown in FIGS. 7and 10 may be decreased or the horizontal wires may even be eliminated;in the case of the alternative embodiment shown in FIG. 8, the number ofvertical wires in the scrim 212 may be reduced or even eliminated. Thescrim is provided only with enough wires running in a directionperpendicular to the direction of the current to provide the amount ofdurability required for a particular application.

The individual cells 206A, 206B, 206C and 206D are filled with anelectroltye (not shown), which can be either a liquid or a gel. Thecells are also provided with separator 218, made of C glass, and a fullyoxidized pad, which acts as a "sponge" to hold electrolyte. Theseparators 218 are thick enough that they actually contact the activematerial on the scrim 212, facilitating their function of helping tohold the active material in place by sandwiching the active materialbetween the separator 218 and the plate 198. In the case of scrims 212Aand 212D, the separator 218 helps to hold the active material in placebetween the separator 218 and the end walls of the battery case 204.

The cells 206D and 206A, at the negative and positive ends of thebattery case 204, respectively, are provided with scrims 212D and 212A,respectively. These scrims 212D and 212A are terminated at their topedge on bus bars 220 and 222, respectively, sealed in glass,polypropylene or other plastic, or glass in polypropylene. The bus bars220 and 222 may be constructed of lead or, preferably, copper, and thescrims 212D and 212A are soldered or welded to their respective bus bars220 and 222. Bus bars 220 and 222 are provided with posts 224 and 226,respectively, The top 210 of the battery case 204 is provided with acover 228, which could also be provided with a conventional vent hole(not shown) as is known in the art.

Referring to FIG. 13, there is shown an alternative embodiment of thebiplate battery of FIGS. 9 and 10, in which the various parts arereferenced, to the extent possible, by the same numerals which are usedin FIGS. 9 and 10. Plates 198' are embedded in walls 202' of batterycase 204', sealing the cells 206A', 206B', 206C' and 206D'. The topedges 208' are embedded in the top 210' of battery case 204' tocompletely seal the cells 206A', 206B', 206C' and 206D'.

A scrim 212' is woven and applied to the plates 198' in much the samemanner as shown in FIGS. 7 and 8, but the wires of scrim 212' are notcontinuous around the edges 200' or the top edges 208' of plates 198'.Electrical conductivity between cells is provided by connectors 207',which may be constructed of copper or aluminum, to which scrims 212' areconnected. To save additional weight in applications which do notrequire high current output, connectors 207' may be eliminated and thewires of scrims 212' may simply be twisted, soldered or electroplatedtogether. In the embodiment shown in FIG. 13, connectors 207' areisolated from chemical attack by the electrolyte (not shown) containedin cells 206A', 206B', 206C' and 206D', consequently it is not necessaryto construct connectors 207' from the composite wire of the presentinvention having a highly conductive metal core and a lead coating toresist attack by the acid electrolyte. Connectors 207' are isolated fromthe electrolyte by top 204', and may be embedded in the material makingup the top 210' or, as shown in FIG. 13, in another material such as thesilicone rubber inserts 209'. Both top 210' and inserts 209' may beconstructed of a variety of other materials as discussed above withreference to FIGS. 9 and 10.

The individual cells 206A', 206B', 206C' and 206D' are filled with anelectrolyte, which can be either a liquid or a gel (also known as astarved immobilized or recombinant electrolyte). When a gel electrolyteis used, the battery constructed in the manner shown in FIG. 13 isparticularly well adapted to applications in which the battery will bevibrated or even inverted because the electrolyte cannot spill out ofthe cells. Each of the cells, 206A', 206B', 206C' and 206D' is providedwith a separator 208' which contacts the paste of active material (notshown) which is applied to scrims 212' on both sides of each plate 198,and to the scrims 212A' and 212D' at the ends of battery case 204'.

Scrims 212A' and 212D' are terminated at their top edge on bus bars 220'and 222', respectively, sealed in the inserts 209'. The bus bars 220'and 222' may be constructed of lead or, preferably, copper, and thescrims 212D' and 212A' are soldered or welded to their respective busbars 220' and 222'. Bus bars 220' and 222' are provided with posts 224'and 226', respectively. The top 210' of the battery case 204' isprovided with a cover 228', which may be sealed if a gel electrolyte isused or provided with a conventional vent hole (not shown) as is knownin the art.

Examples of the benefits of the present invention are as follows. Copperbus wire of 18 AWG (0.040 inches in diameter) was coated with a 0.005inch layer of lead to make a composite bus wire of 0.050 inches indiameter, and the internal lead straps and connectors of a commerciallyavailable, heavy duty, golf cart size, 6 volt deep cycle battery werereplaced with this composite wire. A total of 2.57 pounds of internallead straps and connectors were replaced with 0.31 pounds of compositebus wire of equal current capacity, a connector weight savings ofapproximately 88%. The resulting battery has performance characteristicswhich are at least equal in all respects to the performance of theunmodified battery. Further, the bus bars constructed in this manner aresmaller in diameter than the conventional straps and connectors, makingpossible a more compact battery with equal capacity.

Another heavy duty, golf cart size, 6 volt deep cycle battery wasmodified by replacing its grids with grids constructed as shown in FIG.14. The scrim was woven from a composite wire of 0.020 inches indiameter with a C glass core 0.012 inches in diameter with a 0.004 inchthick layer of lead coated onto it. The bus wire frame was a lead/copper(18 AWG) composite wire with a diameter of 0.050 inches and a 0.005 inchthick layer of lead. The 69 grids which were replaced weighed a total of16.33 pounds, excluding active material paste, and the grids constructedaccording to the teachings of the present invention which replaced thoseconventional grids weighed 4.08 pounds, excluding active pastematerials, resulting in a grid weight savings of approximately 75%. Themodified battery performed at least as well as the unmodified battery,and in some performance characteristics, it has exceeded thecapabilities of the unmodified battery. For instance, the modifiedbattery produces approximately 25% greater amp hours than the unmodifiedbattery at the same discharge currents. The gross wet weight of thebattery was reduced from about 65 pounds to about 49 pounds, a weightsavings of approximately 25%. In other tests, 12 volt lead acid aircraftbatteries modified in the same way indicate approximately a 30%reduction in weight (25 pounds each down to about 17 pounds wet weight)and higher total charge capacity at equivalent discharge rates.

As stated above, the composite lead-coated wire of the present inventionmay be woven into a scrim for use as an electrode grid. A 0.015 inchdiameter lead coated wire with a 0.008 inch copper wire core isapproximately five and one half times more conductive than a 0.015 inchdiameter lead coated wire with a glass core. Aluminum wire has also beenused as a core material, and it is expected that other highly conductivemetals such as silver, gold, nickel and tantalum may likewise beutilized for this purpose. Each core metal has advantages anddisadvantages. For instance, the lead to copper bond is excellent, butthe aluminum to lead bond is relatively poor. However, the aluminum corecomposite wire is much lighter than copper core composite wire,indicating that an aluminum core composite wire may be the constructionwhich is preferred for applications in which light weight is moreimportant than durability. Copper core composite wire is smaller indiameter at equal current ratings, making thinner grids, and therefore amore compact battery, possible. Silver and gold are excellentconductors, but their price is so high as to restrict their use tospecial applications.

Of special importance is the fact that a scrim woven from a lead-coated,wire having either a fibrous core or a core of highly conductive metalretains its flexibility and can be rolled into tight spiral cells,making possible a high current, rechargeable lead-acid battery in sizesas small as "AA", something which is not possible with stamped, die cutor expanded lead grids.

Several "AA" size batteries have been constructed according to theteachings of the present invention and tested at currents of 10 ampsdischarge. The grids are shown in FIG. 17, and are constructed of ascrim 230 woven from a 0.020 inch diameter composite wire with a 0.012inch diameter C glass core and a 0.004 inch thick coating of lead. Theconductor 232 used to remove current from the grid cloth is a compositewire of 0.028 inches in diameter having a 24 AWG copper bus wire core of0.020 inches in diameter with a coating of lead extruded onto it whichis 0.004 inches thick. The composite bus wire is soldered to thecomposite grid cloth 230 all around the ends 234 of the wires making upthe grid 230. The bus wire may be eliminated for low currentapplications, and any one of the configurations of conductor and gridcloth shown in FIGS. 14-18 may be utilized for certain batteryapplications.

Referring to FIG. 19, there is shown a pair of electrodes 236,constructed as shown in FIG. 17, wound in a tight spiral, with aseparator 238 interposed between them. An alternative construction ofthe cell is shown in FIG. 20. FIG. 22 shows the electrodes 236 andseparator 238, before they are wound into the spiral construction shownin FIG. 19, as they would be assembled into a casing 240. The casing 240is sealed with cap 242, and casing 240 and 242 are provided withconnectors 244. For purposes of clarity, the paste of active materialand the electrolyte are not shown in FIGS. 19, 20 and 22. In a preferredembodiment, the electrolyte is a starved immobilized or recombinant gelelectrolyte (also known as a suspended electrolyte) to prevent therelease of gas during the charging of the battery. The connectors may beof conventional bus wire construction, but preferably are constructed ofa composite wire with a copper or aluminium core as described above. Thegrid cloth in the chimney portion 245 of electrodes 236 can be twistedand threaded through cap 242 for use as a connector rather than usingthe separate connectors 244 as shown in FIGS. 19-22. Although theelimination of connectors 244 saves some weight, the ability of thetwisted chimney 245 to conduct current is less than the conductivity ofthe composite wire bus bars having a core of highly conductive metal.Consequently, such a construction is preferred for applications in whichlow weight is of primary concern rather than the ability of the batteryto deliver power.

Four of the cells shown in FIGS. 19 and 22, each of which is capable ofproducing about 2.2 volts, can be assembled into the battery case of aconventional nine volt battery as shown in FIG. 21. Battery case 246 isshown in shadow lines to show the internal construction of the battery,which is comprised of four cells 247 wired in series by connectors 244.Connectors 248 terminate in a conventional positive electrode 250 andnegative electrode 252.

Batteries in sizes smaller than "D" size and in conventional nine voltsize may also be constructed of cells constructed in the biplate designshown in FIGS. 9 and 10. Each casing 246 contains a number of cells withscrims such as the scrims shown at 212 in FIGS. 9 and 10 looping up overthe tops of the plates in the same manner as scrims 212 loop over thetop edge 208 of the plates 198 shown in FIGS. 7 and 8. Separators areprovided the same as the separators 218, and bus bars and posts are usedto conduct current and provide terminals in the same manner as the busbars 220 and 222 and the posts 224 and 226 of FIGS. 9 and 10.

The present invention is also directed to the cabled composite wireshown in FIG. 23, and indicated generally at 254. Cabled composite wire254 is comprised of several composite wires 256 constructed according tothe teachings of the present invention and a lead sheath 258. The wires256 are comprised of a core material 260 with a lead coating 262 asdescribed above. The core material 260 can be either a fibrous materialsuch as E glass, C glass, carbon or aramid fibers as discussed above, ora highly conductive metal such as aluminium or copper. In a preferredembodiment, ten composite wires 256 of 0.020 inches in diameter andhaving a C glass core were coated with a sheath of lead of approximately0.010 inches in the thickness. The cabled composite wire was utilized asa high current, slow blow fuse material.

The composite wires 256 may be twisted, plied or braided before sheath258 is applied to increase the tensile strength of cable 254. The leadsheath is applied by running the composite wires 256 through theapparatus of FIGS. 1 and 2 using a die assembly having dies withapertures of sufficiently large diameter to pass the composite wires 256and to coat those wires 256 with the lead sheath 258 of desiredthickness. For instance, to make the preferred cabled composite wiredescribed above, an entry die with an aperture of 0.093 inches indiameter was used with an exit die having an aperture of 0.113 inches indiameter, the dies being spaced approximately 0.010 inches apart. Anextrusion pressure of from about 30,000 to about 40,000 PSI±25% wasused, and the temperature in the die carrier was maintained at about250° to 300° F. Cables have been made with as few as 6 or as many as 12lead-coated fibers.

Cables constructed according to the teachings of the present inventioncan be tailored for particular applications. For instance, theperformance characteristics of the cable change depending upon the massof the lead applied to the lead-coated fibers and the type of corefiber. An increase in the mass of the lead sheath which is applied tothe lead-coated wires will, for instance, result in a cable which willnot blow as quickly as a cable with less lead applied to it. Further,the increased strength of the cable, which results from the use of corematerials such as E glass or synthetic fibers, allows an increase inproduction speeds as well as making the fuse material easier to handle.

It will be understood that various modifications and changes may be madein the present invention by those of ordinary skill in the art who havethe benefit of this disclosure. All such changes and modifications fallwithin the spirit of this invention, the scope of which is measured bythe following appended claims.

What is claimed is:
 1. Apparatus for coating elongated core materialwith metal, comprising:a compression chamber, for receiving metal forextrusion and having an extrusion outlet; an extrusion die assemblydisposed for communication with the extrusion outlet of the compressionchamber, and for receiving therethrough an elongated core material to becoated; and a piston disposed within the compression chamber, forcompression driving metal through the extrusion outlet to the dieassembly; said piston having spaced annular lands defining acircumferential seal area facing the inner wall of the compressionchamber for receiving metal to form a seal against the wall andsubstantially prevent leakage of metal past the piston duringcompression; said piston including an internal passage between thecircumferential seal area defined by the lands and the end of the pistonthat engages the metal in the chamber to admit metal to the seal area.2. The apparatus of claim 1 wherein the passage comprises a transverseopening through the piston between the lands and an opening through thepiston end which extends to the transverse opening.
 3. The apparatus ofclaim 1 wherein said extrusion die assembly includes:first and seconddie members, each having an aperture for receiving a passage ofelongated core material; and a die separator disposed between the firstand second die members establishing alignment of the apertures andseparation of the apertures to be substantially equal to the radius ofthe thickness of the metal coating to be applied to the core material.4. The apparatus of claim 1 wherein said extrusion die assemblyincludes:an entrance die and an exit die, the dies having oppositelyfacing tapered end portions with apertures for spaced-apart, coaxialalignment for passage of elongated core material; a die separatorcomprising a tubular member having the dies held therein to establish aspace between the end portions and having an aperture through the sidewall to admit extruded metal into the space between the dies; and a dieholder holding the dies and die separator therein including an elongatedbarrel with an aperture through the side wall in alignment with both theaperture in the die separator and the extrusion outlet of thecompression chamber, and having a member for retaining the dies and dieseparator within the barrel.
 5. The apparatus of claim 4 wherein the dieholder is detachably mounted to the compression chamber.
 6. Theapparatus of claim 1 wherein the extrusion die assembly includes:anentry die having an aperture in the range of 0.010 inch to 0.021 inchdiameter; and an exit die having an aperture in the range of 0.015 to0.028 inch diameter.